GMES8 GCES8 Service Manual

52
SERVICING
S-308 CHECKING HOT SURFACE IGNITOR
120V Mini Igniter Single Stage - furnaces use a 120V car-
bide mini igniter for ignition. (part# 20165703) or a
Silicon Nitride igniter (part# 0130F00008) The normal
operating temperature is approximately 2550°F - 2876°F.
D
ISCONNECT
ALL
POWER BEFORE SERVICING.
WARNING
1. Remove burner compartment door to gain access to the
ignitor.
2. Ignitor cool - approximately 70 - 77°F.
3. Disconnect the ignitor from the Ignition Control.
4. Using an ohmmeter measure the resistance of the ignitor:
Mini Igniter : Carbide Mini Igniter should read between
30 to 300 ohms.
5. Reconnect ignitor.
120V Silicon Nitride Igniter - furnaces with a 120V sil-
icone nitride igniter; The normal operating temperature
is approximately 2156°F-2678°F. At room temperature
the igniter ohm reading should be from 37-68 ohms.
L
INE VOLTAGE NOW PRESENT
WARNING
6. After checking and/or replacing of hot surface ignitor,
reinstall burner compartment door and verify proper unit
operation.
S-309 CHECKING FOR FLASHBACK
Flashback will also cause burning in the burner venturi, but is
caused by the burning speed being greater than the gas-air
ow velocity coming from a burner port.
Flashback may occur at the moment of ignition, after a burner
heats up or when the burner turns off. The latter is known
as extinction pop.
Since the end results of ashback and delayed ignition can
be the same (burning in the burner venturi) a denite attempt
should be made to determine which has occurred.
If ashback should occur, check for the following:
1. Improper gas pressure - adjust to proper pressure (See
S-307 CHECKING GAS PRESSURE)..
2. Check burner for proper alignment and/or replace burner.
3. Improper orice size - check orice for obstruction.
S-310 CHECKING PRESSURE SWITCH
The pressure switch a safety device to prevent the combus-
tion cycle from occurring with inadequate venting caused by a
restricted or blocked vent pipe on the 80% and 90% furnaces.
1. Remove burner compartment door to gain access to
pressure switch(es).
2. Remove wires from the pressure switch(es) electrical
terminals.
3. Using a VOM check from common terminal to NC (Nor-
mally Closed) - should read open.
If switch reads as above proceed to Step 4, otherwise re-
place control.
4. Remove the pressure control hose from the control and
interconnect with an inclined manometer as shown in the
following gures.
ID Blower Pressure Switch
Negative Pressure Measurement
(80% Upow Single-Stage Furnace Shown,
Counterow Similar)